1. My mother writes letters to her friends every week.
2. My mother is writing letter to her friends now.
3. My mother wrote letters to her friends yesterday.
4. My mother will write letters to her friends tomorrow.
5. My mother has already written letters to her friends.
6. My mother was writing letters to her friends at 5 o'clock yesterday.
7. My mother had written letters to her friends by 5 o'clock yesterday.
8. My mother has been wruting letters to her friends the whole day.
9. My mother had been writing letters to her friends the whole day yesterday.
10. My mother will be writing letters to her friends at 5 o'clock tomorrow.